Find divisors for a matrix with alternate scaling
find_matrix_divisors(M, seats_cols, seats_rows, round_func)
list of divisors (column and row)
votes_matrix
target seats for each column
target seats for each row
rounding function. Called like
round_func(M/row_divisors/col_divisors)
, divisors are applied row/col-wise with
divide_votes_matrix()
.